This is a collaborative post by Chloe Genter and guest author Masumi Takeuchi. Masumi is a conservator from Tokyo, working in private practice in Japan. She is currently a Visiting Conservator at the Library of Congress’ Conservation Division working on book and paper treatment projects.
Recently, a cartoon of a famous 19th century British jockey, Tom Loates from the Caroline and Erwin Swann collection of the Prints and Photographs Division at The Library of Congress received much needed treatment. Drawn in pencil on blue paper with watercolor washes in grey, red, white, blue and black, the cartoon is typical of the work of the artist and caricaturist, Sir Leslie Ward.
When Masumi received the drawing, it was attached to a poor-quality backing matboard and had thick adhesive along the edges on the recto side, suggesting that a window mat was adhered on top. The paper was also lightly discolored in the mat opening, and there were three horizontal brown stains in the upper section where the paper was more deteriorated and brittle. One of these stains that went through the drawing was a darker brown than the others and had a 7cm tear starting at the right edge that was bulging due to the partial detachment from the back board. The back board also had condition issues, as it was brittle overall, with dark brown stains and embrittlement in the same area of the stains on the blue paper. These stains were most likely caused by wooden slats when it was framed prior to coming to the Library.
Aside from the glaring discoloration of the board and adhesive residues, Masumi noticed the presence of clear crystals on the grey jacket of the figure in the areas where the paper was stained dark brown. When examined under a microscope, these crystals were tiny, clear, white particles which appeared to be in the fibers. Upon examination with ultraviolet (UV) illumination, the white trousers, white shirt, the bottom of the grey jacket, the red vest and the red helmet fluoresced suggesting the possible use of the pigment zinc white (zinc oxide). However, the areas where there were crystals did not fluoresce. The crystals were assumed to be some other form of a zinc salt, presumably from a reaction between the zinc white pigment, acidic degradation products from the backing board and wood frame, and a humid environment. The reaction of these materials seems to have resulted in “efflorescence”, the phenomena in which crystalline or powdery deposits of water-soluble salts appear on the surface of objects.